The present invention relates to the manufacture of objects. More particularly, the invention provides a technique including a device for planarizing a film of material of an article such as a semiconductor wafer. However, it will be recognized that the invention has a wider range of applicability; it can also be applied to flat panel displays, hard disks, raw wafers, MR heads, precision optics and lens, and other objects that require a high degree of planarity.
The fabrication of integrated circuit devices often begins by producing semiconductor wafers cut from an ingot of single crystal silicon which is formed by pulling a seed from a silicon melt rotating in a crucible. The ingot is then sliced into individual wafers using a diamond cutting blade. Following the cutting operation, at least one surface (process surface) of the wafer is polished to a relatively flat, scratch-free surface. The polished surface area of the wafer is first subdivided into a plurality of die locations at which integrated circuits (IC) are subsequently formed. A series of wafer masking and processing steps are used to fabricate each IC. Thereafter, the individual dice are cut or scribed from the wafer and individually packaged and tested to complete the device manufacture process.
During IC manufacturing, the various masking and processing steps typically result in the formation of topographical irregularities on the wafer surface. For example, topographical surface irregularities are created after metallization, which includes a sequence of blanketing the wafer surface with a conductive metal layer and then etching away unwanted portions of the blanket metal layer to form a metallization interconnect pattern on each IC. This problem is exacerbated by the use of multilevel interconnects.
A common surface irregularity in a semiconductor wafer is known as a step. A step is the resulting height differential between the metal interconnect or silicon oxide and the wafer surface where the metal has been removed. A typical VLSI chip on which a first metallization layer has been defined may contain several million steps, and the whole wafer may contain several hundred ICs.
Consequently, maintaining wafer surface planarity during fabrication is important. Photolithographic processes are typically pushed close to the limit of resolution in order to create maximum circuit density. Typical device geometries call for line widths on the order of 0.5 xcexcm. Since these geometries are photolithographically produced, it is important that the wafer surface be highly planar in order to accurately focus the illumination radiation at a single plane of focus to achieve precise imaging over the entire surface of the wafer. A wafer surface that is not sufficiently planar, will result in structures that are poorly defined, with the circuits either being nonfunctional or, at best, exhibiting less than optimum performance. To alleviate these problems, the wafer is xe2x80x9cplanarizedxe2x80x9d at various points in the process to minimize non-planar topography and its adverse effects. As additional levels are added to multilevel-interconnection schemes and circuit features are scaled to submicron dimensions, the required degree of planarization increases. As circuit dimensions are reduced, interconnect levels must be globally planarized to produce a reliable, high density device. Planarization can be implemented in either the conductor or the dielectric layers.
In order to achieve the degree of planarity required to produce high density integrated circuits, chemical-mechanical planarization processes (xe2x80x9cCMPxe2x80x9d) are being employed with increasing frequency. A conventional rotational CMP apparatus includes a wafer carrier for holding a semiconductor wafer. A soft, resilient pad is typically placed between the wafer carrier and the wafer, and the wafer is generally held against the resilient pad by a partial vacuum. The wafer carrier is designed to be continuously rotated by a drive motor. In addition, the wafer carrier typically is also designed for transverse movement. The rotational and transverse movement is intended to reduce variability in material removal rates over the surface of the wafer. The apparatus further includes a rotating platen on which is mounted a polishing pad. The platen is relatively large in comparison to the wafer, so that during the CMP process, the wafer may be moved across the surface of the polishing pad by the wafer carrier. A polishing slurry containing chemically-reactive solution, in which are suspended abrasive particles, is deposited through a supply tube onto the surface of the polishing pad.
CMP is advantageous because it can be performed in one step, in contrast to prior planarization techniques which tend to be more complex, involving multiple steps. For example, planarization of CVD interlevel dielectric films can be achieved by a sacrificial layer etchback technique. This involves coating the CVD dielectric with a film which is then rapidly etched back (sacrificed) to expose the topmost portions of the underlying dielectric. The etch chemistry is then changed to provide removal of the sacrificial layer and dielectric at the same rate. This continues until all of the sacrificial layer has been etched away, resulting in a planarized dielectric layer.
Many other limitations, however, exist with CMP. Specifically, CMP often involves a large polishing pad, which uses a large quantity of slurry material. The large polishing pad is often difficult to control and requires expensive and difficult to control slurries. Additionally, the large polishing pad is often difficult to remove and replace. The large pad is also expensive and consumes a large foot print in the fabrication facility. These and other limitations still exist with CMP and the like.
What is needed is an improvement of the CMP technique to improve the degree of global planarity and uniformity that can be achieved using CMP.
The present invention achieves these benefits in the context of known process technology and known techniques in the art. The present invention provides an improved planarization apparatus for chemical mechanical planarization (CMP). Specifically, the present invention provides an improved planarization apparatus that provides multi-action CMP, such as orbital and spin action, to achieve uniformity during planarization. The present invention further provides conditioning of the polishing pad for subaperture chemical mechanical planarization wherein the polishing pad has a contact area with the workpiece that is smaller than the size of the workpiece.
In accordance with an aspect of the present invention, a chemical-mechanical planarization apparatus for planarizing an object comprises a platen assembly for holding an object having a target surface to be planarized. A polishing pad is configured to contact the object during planarization with a contact portion over a contact area which is smaller in area than the target surface. The polishing pad has a noncontact portion which is not in contact with the object during planarization. The polishing pad is movable relative to the object to move the noncontact portion in contact with the object and move the contact portion out of contact with the object. A conditioner is configured to condition the noncontact portion of the polishing pad.
In some embodiments, the polishing pad is annular. In other embodiments, the polishing pad has a solid circular surface for contacting the target surface with at least a portion thereof. The noncontact portion of the polishing pad may overhang the target surface of the object, and the conditioner is disposed below the noncontact portion. The polishing pad may be selected from the group consisting of a pad for use with a loose abrasive, a pad with a fixed abrasive, and a grinding pad. The polishing pad may be rotatable relative to the object to move the noncontact portion in contact with the object and move the contact portion out of contact with the object. The object may be rotatable around an axis perpendicular to the target surface.
In specific embodiments, the conditioner is configured to condition the noncontact portion of the polishing pad during planarization of the object by the polishing pad. The conditioning may be continuous or intermittent. The conditioner may comprise a conditioning plate, such as a diamond conditioning disk. The conditioning plate may be stationary. The conditioning plate may be rotatable. The conditioning plate may be an annular plate surrounding the target surface of the object. The annular plate may be stationary, or may be configured to rotate around the object or oscillate in rotation relative to the object. The annular plate may form a retaining ring around the target surface of the object. The annular plate may include an annular band adjacent to and surrounding an edge of the target surface, where the annular band performs no conditioning on the target surface.
In some embodiments, the polishing pad is movable in translation across the target surface of the object and the conditioning plate may move in translation with the polishing pad. The conditioner may comprise a pressurized fluid to be directed to the noncontact portion of the polishing pad. The pressurized fluid may be ultrasonic energized. The pressurized fluid may comprise at least one of deionized water, KOH, and a slurry.
In accordance with another aspect of the invention, a method for planarizing an object by chemical mechanical planarization comprises placing a contact portion of a polishing pad in contact with a target surface of the object to be planarized over a contact area which is smaller in area than the target surface. A noncontact portion of the polishing pad which is not in contact with the target surface of the object is conditioned. The polishing pad is moved relative to the target surface of the object to move the noncontact portion in contact with the target surface of the object and move the contact portion out of contact with the target surface of the object.
In some embodiments, the noncontact portion of the polishing pad comprises dislodging particles from a surface thereof. Conditioning the noncontact portion of the polishing pad may comprise placing a conditioning plate in contact with the noncontact portion. The polishing pad may be moved in translation across the target surface of the object and the conditioning plate may be moved in translation with the polishing pad. Conditioning the noncontact portion of the polishing pad may comprise directing a pressurized fluid to the noncontact portion. The noncontact portion of the polishing pad may be conditioned during planarization of the object by the polishing pad, and the conditioning may be continuous during planarization of the object.
In specific embodiments, the polishing pad is rotated relative to the object to move the noncontact portion in contact with the target surface of the object and move the contact portion out of contact with the target surface of the object. The object may be rotated around an axis perpendicular to the target surface. An abrasive may be delivered to the contact area between the polishing pad and the target surface of the object.